This is a simple prank for Trick-or-treaters. It only requires a window alarm and an Altoids tin. I picked up an alarm at the dollar store. For a buck a piece you can make one for every trick-or-treater in the neighborhood (just the people you know).

Step 1:

First, clean the tin so the double sided tape that comes with the alarm can stick. You will also need to test out the alarm (it was only a dollar so quality is not the best). Try to resist from quoting Boondock Saints while looking at the criminal in the picture.

Connor: Okay, Roc...
[Connor looks at him and laughs; his mask is badly put on]
Rocco: What? You guys got masks.
Murphy: You look like Mush Mouth from Fat Albert.
[as they keep giggling, Rocco takes his mask off]
Rocco: Fine! F**k it. When we're done, she can ID me. I don't care. Just trying to be professional, but nooooo...
Connor: It looks fine!
Rocco: F**k it.
Connor: Now shut the F**k up, you look good. Put it on! You look F**kin' scary, man!
[Rocco puts his mask on, again badly]
Connor: [trying not to laugh] Now Roc, are you sure that you're obee-kay-bee?

Step 2:

Place the sensor centered on the lid and close to the edge, like in the picture. It comes with a sticky backing so peel off the wax paper and stick it to the lid. It is not important if you are off a bit.

Next is the loud part, place the alarm body close to where you think it should go (no tape yet) and turn it on.The alarm will sound until you close the lid. After it's closed, it should shut off, but if it does not then just lightly shake it into place until it shuts off. Without moving the alarm body, open the lid and trace around it so you can remove the wax paper and stick it into the same place.